9 Way 10 Amp boxed PSU PTC Fuses Surge Protected. POWER SUPPLIES DIRECT range of multi way metal cased PSUs (STP-18WAYBOX & STP-9WAYBOX) use the latest technology PTC fuses, eliminating replacing fuses after overvoltage or short circuit occurs When traditional fuses are being used for over current protection it can only protect once then it must be replaced. The PTC resettable fuse is a new-type of over current protection element which has two functions providing over current protection and automatic reset.